Affiliation:
1. Fakultät für Mathematik Karlsruher Institut für Technologie (KIT) Karlsruhe Germany
2. Fakultät für Mathematik Technische Universität Dortmund Dortmund Germany
Abstract
We study the Helmholtz equation with periodic coefficients in a closed waveguide. A functional analytic approach is used to formulate and solve the radiation problem in a self‐contained exposition. In this context, we simplify the non‐degeneracy assumption on the frequency. Limiting absorption principles (LAPs) are studied, and the radiation condition corresponding to the chosen LAP is derived; we include an example to show different LAPs lead, in general, to different solutions of the radiation problem. Finally, we characterize the set of all bounded solutions to the homogeneous problem.